01 Gearing Up: How Cetane Numbers Boost Your Diesel Engine's P… • 02 Driving with Confidence: Mastering the Use of Vehicle Light… • 03 Why Disconnecting Your Car Battery for Storage is a Good Ba… • 04 Engine CC: What It Is and How to Calculate It • 05 How A Simple Mistake At The Gas Pump Could Destroy Your Eng… • 06 What are the signs of a suspension problem? • 07 The Ultimate Guide to Inspect a Used Car Before Buying • 08 The One Mistake People Make When Skipping Gears in Manual T… • 09 This Is Why Your Car Won’t Start Even With A New Battery • 10 Why are not all tires on a car the same width? •

DTC codes / P07xx · Transmission / P071D

P071DTransmission Mode Switch B Circuit

P071D indicates that the transmission control module has detected an abnormal signal from the transmission mode switch B circuit, which is used to select different driving modes such as sport or economy. The computer compares the switch input to expected values and sets this code when the voltage or resistance falls outside the programmed range for a calibrated time.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The check engine light or transmission warning light illuminates on the dashboard.
  • The transmission may stay in a single mode and not respond to mode selection changes.
  • The driver may notice harsh or delayed shifting as the transmission defaults to a limp mode.
  • Some vehicles may display a message indicating transmission mode unavailable or a similar warning.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.
  • The mode indicator on the instrument cluster may flash or not illuminate at all.

Common causes, most likely first

  1. Faulty transmission mode switch B, worn contacts or internal failure.
  2. Damaged or corroded wiring harness or connector at the switch or transmission control module.
  3. Open or short circuit in the signal or ground circuit for the mode switch.
  4. Water intrusion or contamination in the switch connector causing intermittent signals.
  5. Transmission control module software glitch or internal fault, though less common.
  6. Loose or improperly seated connector pins at the transmission control module.
  7. Aftermarket accessories or poor previous repairs interfering with the circuit.

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes and freeze-frame data to confirm P071D is the primary fault.
  2. Inspect the transmission mode switch and its connector for physical damage, corrosion, or loose pins.
  3. Check the switch operation using a multimeter to verify continuity or voltage changes in each mode position.
  4. Perform a wiggle test on the wiring harness while monitoring switch data to detect intermittent faults.
  5. Check for technical service bulletins or software updates for the transmission control module that address mode switch codes.
  6. If the switch tests bad, replace it and clear codes to verify the repair.
  7. If the circuit tests good but the code persists, diagnose the transmission control module and its programming.

What the mode switch code hides

  • A common misdiagnosis is replacing the transmission mode switch when the real problem is a chafed wire in the harness near the transmission, which only shows up during engine movement.
  • The code can set intermittently due to a poor ground connection at the transmission case, so always verify ground integrity before condemning the switch.
  • Some vehicles use the same switch for multiple functions, so a failure may also affect cruise control or tow/haul mode without setting additional codes.
  • After replacing the switch, the transmission control module may require a relearn procedure or calibration drive cycle to clear the code permanently.
  • A weak battery or charging system fault can cause spurious mode switch codes because the module may misinterpret voltage fluctuations as switch errors.

Can I keep driving with P071D?

The vehicle is generally safe to drive with P071D because the transmission defaults to a safe mode, but avoid aggressive driving or towing until repaired. If the transmission exhibits harsh shifting or fails to shift, have it inspected promptly to prevent further damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage